Loudspeaker



United States Patent Inventor Vaino Ronka Don Mills, Ontario, Canada Appl. No. 766,931 Filed Oct. 11, 1968 Patented Nov. 24, 1970 Assignee Geonlcs Limited,

Toronto, Ontario, Canada a corporation LOUDSPEAKER 6 Claims, 5 Drawing Figs.

U.S. Cl a. 1s1/0.5; 340/15 Int. Cl. G0lv 1/00 Field of Search 181/05; 3 40/ l 5 [56] References Cited UNITED STATES PATENTS 2,549,464 4/1951 Hartley 181/05 Primary Examiner-Rodney D. Bennett Assistant Examiner-Joseph G. Baxter Attorney-Curtis, Morris and Safford ABSTRACT: A loudspeaker for radiating a relatively narrow band width of acoustical signals about a predetermined frequency. A preferred embodiment of this loudspeaker is made by positioning an earphone between two quarter-wave open ended chambers. Such a loudspeaker advantageously is used with electromagnetic prospecting apparatus and the like.

Patented Nov. 24, 1970 3,542,149

34 IXVLN'I'OK VAINO 'RONKA ATTOR E S LOUDSPEAKER This invention relates generally to loudspeakers, and more particularly to tuned loudspeakers that radiate a relatively narrow band width of acoustical signals about a predetermined frequency, and even more particularly to a loudspeaker that can be made from an earphone.

The loudspeaker of this invention is advantageously used whenever the radiation of an audio signal of a predetermined frequency is required. The operation of certain electromechanical or electromagnetic apparatus requires the radiation of an audio signal of a single frequency. The electromagnetic prospecting apparatus disclosed in copending U. S. Pat. application Ser. No. 632,656 is one example of such equipment with which this invention is advantageously used. In the operation of such equipment, two signals of the same frequency are caused to buck, or cancel, each other. The resultant signal is detected, or observed, for a null. This is achieved by converting the resultant signal being detected into an audio frequency signal which is radiated by an earphone, and the null is found by noting the minimum sound in the earphone. The earphone is used, thusly, to radiate an acoustical signal of only one predetermined frequency.

In such equipment a loudspeaker can be used in place of earphones to radiate the predetermined audio signal. Often a loudspeaker is preferred because there is no need to wear a headband, or an ear insert piece, or to have a wire extending from the apparatus to the earphone. At other times, an earphone may be preferred so that the radiated signal is confined to the ear of the user. Also, an earphone may be preferred because it usually is less costly than a loudspeaker. Ideally, because there are relative advantages and disadvantages in using one device and not the other, the choice of either an earphone or a loudspeaker should be available without a great additional cost to the user of the prospecting equipment mentioned above. Even more ideally, also without a great additional cost, a person using the equipment should be able to use a loudspeaker or an earphone interchangeably to obtain the benefits of both.

Accordingly, an object'of this invention is to provide an efficient, simple, lightweight, low cost, loudspeaker suitable for use with electromechanical or electromagnetic apparatus requiring the radiation of an audio signal of only one predetermined frequency that costs only slightly more than a suitable earphone and that can be used interchangeably for an earphone to radiate an audio signal of a predetermined frequency. Another object of this invention is to provide such a loudspeaker that is responsive to a relatively narrow band width of acoustical signals and that, accordingly, eliminates unwanted signals outside the bandpass of the loudspeaker.

This and other objects are achieved in accordance with the invention by positioning a low volume electroacoustical transducer between two quarter-wave open ended chambers. This electroacoustical transducer advantageously can be the same earphone as the one that can be used interchangeably with the loudspeaker of this invention. Accordingly, another object of this invention is to provide a loudspeaker suitable for use to radiate a signal ofa predetermined frequency that can be converted from an ordinary earphone.

Other objects and advantages of the invention will be made apparent in the following description and drawing.

In the drawing:

FIG. I is a perspective view ofa loudspeaker constructed in accordance with the teachings of this invention mounted on electromagnetic prospecting apparatus carried by an opera tor;

FIG. 2 is a larger, more detailed view of the loudspeaker shown in FIG. 1 showing only a small broken away portion of the electromagnetic prospecting apparatus of FIG. 1;

FIG. 3 is an exploded view of the loudspeaker shown in FIGS. 1 and 2;

FIG. 4 is a top-plan view of the loudspeaker; and

FIG. 5 is a view ofthe loudspeaker partly in section taken along the line 5-5 of FIG. 4.

A preferred embodiment of the loudspeaker'assembly of the present invention is shown at 10 in FIG. I mounted on electromagnetic prospecting apparatus 12 being hand carried by an operator 14 who is listening to a signal radiating from the loudspeaker unit 10.

This loudspeaker unit 10 is shown in approximately full scale in FIGS. 2 through 5. It has a mounting bracket designated generally by the numeral 16, a resonator chamber or column 39 formed by tube 18, and an earphone 20. Mounting bracket designated by the numeral 16 has upper and lower portions 22 and 24 which are clamped together by screws 26 that pass through openings in the upper portion 22 and are threaded into the lower portion 24. This lower portion 24 conveniently is provided with a clamp designated generally by the numeral 28 having a knob 30 that operates a movable clamp element 32 which, in cooperation with another clamp element 33, is adapted to engage a mount piece 34 secured by fastening assembly 35 to the top of the electromagnetic prospecting apparatus 12 (see FIGS 2 and 5).

When the upper and lower mounting bracket portions 22 and 24 are clamped together, under surface 36 of upper portion 22 and upper surface 38 oflower portion 24 define a substantially tubular opening 25, the diameter of which is slightly smaller than the outer diameter of tube 18 so that it may be positioned and clamped therebetween. The upper clamp portion 22 has an opening 40 therein as shown in FIG. 3 which provides a passageway through the bracket and through a corresponding opening 42 in the center of tube 18.

The length of the tube 18 is equal to one-half of the wavelength of the desired audio signal as measured in the media through which the acoustical signal is passing. Thus, this tube 18 defines a resonator chamber 39 of a one-fourth wavelength on each side of signal input opening 42, with both ends 41 and 43 of tube 18 open.

The particular tube for the embodiment shown in dimensioned to resonate a 1.6KI-IZ signal. The tube is' 92.5 mm. long. It has been determined experimentally that a tube of this length, having an inner diameter of 23.5 mm., provides for the most effective result even though it is somewhat shorter than onehalf the wavelength of a 1.6 KHZ signal.

Earphone 20 is a small dynamic earphone of the type normally used with an insert shaped to fit in the users ear, such as is used with hearing aids, small radios and the like, and is connected to the signal source, e.g. the prospecting apparatus 12, by a connecting wire 44.

The earphone 20 is affixed by clip or other suitable at tachment arrangement to upper portion 22 of bracket 16 so thatv the sound output opening 50 in the earphone coincides with the opening 40 of the upper bracket portion 22 and also with aligned feed opening 42 in tube 18. A gasket 54, surrounding opening 50, provides a tight seal between the earphone and the bracket.

In operation a signal received by the electromagnetic prospecting apparatus 12 is converted to an electrical signal in the audio frequency range (e.g. 1.6 KHZ) which is fed through wire 44 to earphone 20.which transforms the electrical signal to a low-volume, high-pressure acoustical signal, i.e. pressure wave in the ambient medium. This pressure wave generated by the earphone 20 passes through opening 50 in the earphone to the center of resonating chamber 39. The signal is resonated in the chamber and is coupled to the ambient air at each of the open ends 41 and 43 as a relatively low-pressure, highvelocity, high-volume wave.

It should be appreciated that a tube, longer on either or both ends by one or more one-half wavelength sections, will resonate the same signal resonated by the tube described above. Also, it should be appreciated that tubes of other lengths can be used to resonate signals of other frequencies.

The embodiment shown herein, is conveniently called a monotonic speaker because it radiates only a relatively small band width of acoustical signals producing only a single, Le. mono", tone. It employs a small insert type earphone, but it should be realized that other types and other size earphones or any suitable electroacoustical transducer may be used. The transducer unit used-in the embodiment shown was chosen because it can be used advantageously, apart from the loudspeaker, as'an earphone.

it should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set forth in the following claims.

lclaim: I

1. A loudspeaker arrangement for radiating an acoustical signal comprising, in combination, an electroacoustical transducing means for. transforming an electrical signal of a predetermined frequency to a relatively low-volume, high pressure acoustical signal," means defining an' elongated resonator chamber having open ends and a signal-feed opening leading into said chamber, said chamber having a length approximately equal to one or more one-half wavelengths of the acoustical signal to be resonated, said defined signal-feed opening leading into said chamber at a' point located between the open ends of said chamber and spaced an odd number of quarter wavelengths from the open ends of said chamber, and means for coupling said acoustical signal from said electroacoustical transducing means to said feed opening and therethrough into said chamber wherein said relatively lowvolume, high-pressure acoustical signal is resonated and thus transformed into a relatively high-volume, low-pressure acoustical signal, whereby apparatus is provided to transform an electrical signal to an acoustical signal, to resonate said acoustical signal and to couple said signal to the ambient air through which it is to radiate.

2. A loudspeaker as defined in claim 1 wherein said means defining a chamber having open ends and a signal-feed openin'gis a tube having a length equal to one-half the wavelength of the acoustical signal to be resonated and wherein said defined signal-feed opening is located at a point spaced one quarter wavelength from one end.

3. A loudspeaker arrangement as described in claim 2 wherein said tube is held by a mounting bracket and wherein said electroacoustical transducing means is affixed to said bracket.

4. A loudspeaker arrangement as described in claim 3 wherein said electroacoustical transducing means is an earphone.

5. A loudspeaker arrangement as described in claim 4 for use with electromagnetic prospecting apparatus, wherein said tube is about 93 mm. long and has an inner diameter of about 6. A loudspeaker arrangement for radiating an acoustical signal comprising,in combination, an earphone with an audio outlet opening, a cylindrical tube having open ends and a signal feed opening located in the tube midway between the open ends, said tube defining an elongated resonator chamber having a length approximately equal to one-half the wavelength of the acoustical signal to be resonatedand further defining quarter wave chambers on each side of said signalfeed opening, and a mounting bracket to support said tube and said earphone, said mounting bracket having an opening therein, said signal-feed opening, said opening in said mounting bracket and said audio outlet opening being aligned to define a passageway to couple said acoustical signal from said earphone to said resonator chamber, whereby apparatus is provided to transform an electrical signal to an acoustical signal, to resonate said acoustical signal and to couple said signal through ambient air to which it is to radiate. 

